High-frequency detector.



G. W. ELM EN.

HIGH FREQUENCY DETECTOR.

APPLICATION FILED NOV. 23. 1915.

1,289,418; Patented Dec. 31, 1918.

mvenfor: Guslaf W E/men.

" UNITED STATES PATENT orrr.

GUSTAF W. ELMEN, OF BOGOTA, NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

HIGH-FREQUEN CY DETECTOR.

Specification of Letters Patent. 7 Patented Dec. 31, 191.8.

Application filed November 23, 1915. Serial No. 62,949.

To all whom'z't may concern:

Be it known that I, GUSTAF IV. ELMEN, originally a subject of the. King of Sweden, who arrived in Philadelphia from Sweden on August 1, 1893, when sixteen years of age, declared my intention of becoming a citizen of the United States on October 5, 1900, and again on April 30, 1915, have been a constant resident of the United States since my arrival, but have not taken out myfinal naturalization papers, am now residing at Bogota, in the county of Bergen and State of New Jersey, and have invented certain new and useful Improvements in- High-Frequency Detectors, of which the following is a full, clear, concise, and exact description.

This invention relates to an apparatus for detecting the presence of oscillatory currents in a conductor, and in particular to a detector of high-frequency oscillations of the typegenerally known in the art as magnetic detector.

WVhen an alternating or pulsatin current traverses a coil having an iron or otIxer magnetic core, a certain amount of energy is lost due to the hysteresis in the iron. This energy must be supplied by the source which causes the iron to pass through the hysteresis cycle, and may be looked upon and expressed as being equivalent to the work done in overcoming a certain amount of resistance, which may be called the effective resistance in the coil due to hysteresis. If W is the total energy per unit of'time and E and I are the voltage and current respectively used in the coil, then w E1=i=R or R g.

R here represents the so-called effective resupplied by a given alternating or pulsating current source, and for this purpose I make use of the discovery that the superposition on the iron or other magnetic core ofan al ternating current of appreciably higher frequency will reduce the energy supplied by the low frequency; that is, it will reduce the area of the hysteresis loop for the low-frequency current. Apparently the high-frequency oscillations act in a manner to shake up the iron molecules and reduce the force required to set them into motion, thus saving low-frequency energy, the energy required to do this shaking-up being supplied by the hi h-frequency source.

In practice I find that it is not necessary that the high-frequency shall be excessively high. I find, for example, that if the lowfrequency is about 15 per second that a highfrequency of 60 per second is sufficient to cause the reduction of the hysteresis loop on the low-frequency side to practically zero.

If the low-frequency is raised, then the highfrequency must be raised correspondingly and may be made very much higher than the low-frequency.

I have found that this effect may be made use of in constructing a sensitive and reliable detector of high-frequency waves by using means which will note a change in the hysteretic energy supplied by the low-frequency source. Heretofore in magnetic detectors use has been'made of the sudden induced effects produced in a receiver circuit when the hysteresis cycle-in a body of iron is broughtpartially or wholly into phase with the magnetiz'ing force by the received high-frequency oscillations. This sudden breaking down of the magnetic condition gives a sharp click or signal in the receiver or translating device which is independent of the frequency of the low-frequency magnetizing force. In my invention, however, I do not primarily make use of this sudden induced electromotive force, but I make use of'the change in the hysteretic energy which must be supplied by the lowfrequency source when high-frequency oscillations are re ceived. This change in the hysteretic energy is equivalent to a change in the effective resistance of the coil surrounding the iron, and

any method for indicating-or measuring this change in effective resistance will be useful.

in indicating the presence of the high-fre-- quency current,

Inasmuch as one of the most sensitive and reliable methods of measuring reslstances or indicating changes in resistances is'the.

Wheatstones bridge, I have made use of such a circuit to carry out my inventlon, and

. made as nearly identical'as possible, any slight difierence in them can be adjusted for by means of the resistances 3 and 4.

this will be better understood by reference to the following specification and accom panying drawings, in which Figure 1 shows one circuit arrangement for detecting the presence of high-frequency oscillations. Fig. 2 shows a modification of this circuit, and

- Figs. 3 and 4: show forms of coils which I which, in general, would be made adjustable.

Connected to the corners A. and 'B of the rectangle is asource 10 of alternating or pulsating current, which source or generator will hereafter be spoken of as the source of low frequency currents or oscillations. Between the corners C and D is connected an indicating or translating device '1 of any suitable form. This translating device may consist of a vibration galvanometer or of a telephone receiver onother device which is responsive to oscillations of the frequency generated by the source 10. Inductively connected to the coil 2 is the coil 15, which forms a part of the receiving system of highfrequency oscillations which are to be detected, such, for example, as are used in.

wireless telegraphy. It is to be understood, however, that the invention is not limited to wireless telegraphy but may be used. wherever it is desirable to show the presence of oscillations of a frequency relatively high as compared to the frequency of source 10.- I have shown'this coil connected at the one end to the aerial 16 and at the other end to the earth at 17.

The c eration of this device is as follows: The bri ge is balanced both for ohmic resistance and for reactance, in a manner wellknown in the art, so that no current shall flow. through the indicating device T. Y In order to assist in this adjustment, it may be desirable to place the non-inductive resistances 5 and 6 in the branches containing the coils l and 2, but these will not. always be necessary, for if the coils l and 2' are Under these conditions, low-frequency oscillations will ass continually through the network, and t e iron cores of the coils, 1 and 2 W111 be caused to pass through a magnetic cycle, and energy will, be consumed because of the hysteresis of the iron. Since the bridge is balanced, however, no current will ass through the translating device T. ien high-frequency oscillations are impressed upon the coil 2 by means of the coil 15, the magnetic condition of the core of this coil will be suddenly brought into phase, wholly or partially, with the magnetizing force. As a result the bridge will be thrown out of balance and an indication will be given at T. lln general this lack of balance is due to two factors, the first of which may be designated as e, and is due to the change in the flux in thecoil 2, giving rise to a sudden induced electromotive force, which causes a flow of current through the device T. In addition to this effect there is a second efiect which may be designated as 0,, and as explained earlier in this specification, is due to the reduction in the hysteretic energy absorbed as a result of the hysteresis cycle through whichthe iron is carried by the low-frequency source 10'. This reduction in the amount of the hysteretic energy represents a reduction in the amount of energy which is consumed in the coil '2, and is therefore equivalent to a reduction in the effective resistance of the coil. lThlS change in at fective resistance produces a lack of balance .in the bridge, and consequently there is a flow through the translating device '1 of current from the source 10. It will beneticed that the first effect e, corresponds to the effect which is ordinarily made use of in magnetic detectors as heretofore constructed and that the edect produced in T is simply a sharp cliblr due to the sudden induced electromotive force. The second effect e however, is independent of this, and is due to a lack of balance in the bridge, as a result of which there will be heard in the telephone receiver T a note which corresponds to the frequency of the generator 10, which note will persist as long as the" coil 2 is subjected to the high-frequency oscillations.

I wish it to be understood that whllel have shown and explained thus far a simplev Wheatstones bridge, that any other network which is adapted to measure inductances may be used. Such a circuit, for example, is

shown in Fig. 2, in which a variable condenser 20 is connected from the point A to some point E on the branch CD, which in this case has a small resistance.

The brid e in this case. is brought into balance sit or by an adjustment of the capacity 20 or by an adjustment of the point of contact E. Having brought th bridge into balance, no current from the generator coils, these will not in device is adapted to be used.

ing an indication by th and the ground connection being made directly to the coil 2, with adjustable contacts, as shown.

While in these two figures above described I have shown the coils 1 and 2 as open core eneral be entirely satisfactory. for it is desirable that the core. of each coil shall be one of low coercive force and high remanence. In order to obtam such a condition, it IS desirable to use a closed core, as shown in Figs. 3 and 4. Furthermore, in order to reduce the eddy currents, these cores should be laminated or stranded in a manner well understood in the art. In Fig. 3 the high-frequency coil is shown as wound upon the core in the same manner as for the coil 2. In Fig. 4 this antenna or high-frequency coil is shown as being wound parallel to the core and preferably embedded. in the center thereof.

It has been found that in this case the effect of the high-frequency oscillations in reducing the hysteresis. loss is as effective as in the coils shown in Fig. 3. Furthermore, it will be noticed that in this Fig. 4 the coil 15 is at all points at right angles to the coil 2, and that therefore there is no induced effect of the coil 15 upon the coil 2. Y

Whatever form of coil is used, it is to be understood that generally the coils 1 and 2 will be as nearly identical as possible in order to facilitate the operation of bringing the bridge into balance, but it is to be understood that this is not essential for the operation of the device.

The frequency of the generator 10 may be varied between wide limits. If the translating device T is to be the ordinary telephone receiver, then it is obvious that the frequency should be within the limits of audibility, and in this case I have found that a frequency of about 800 is very good indeed. If the translating device is a vibration galvanometer or some such device, the fre quency may be made either lower or higher than the limits of audibility, thisbeing determined by the frequency for which the at is claimed is:

v 1. The method which comprises producing a low frequency magnetic flux in a magnetic body and causing an indication by the change produced by a high. frequency flux in thehysteresis energy required to maintain the low frequency flux.

2. The method of detecting high frequency currents which comprises subjecting a magnetic body to the simultaneous magnetizing action of said high frequency currents and a low frequency current and cause variation in the value of the hysteresis energy supplied by the low frequency current during the action of said high frequency currents.

. cause said iron core to 3. A receiving device for high frequency 4. A recelving device comprising a source of electrical energy, a Wheatstone bridge havingan arm comprising a magnetic core connected to said source and means whereby the impedance of said arm is varied.

5. A receiver of high-frequency currents or oscillations comprising a network, one branch thereof containing a coil with an iron core, a source of low-frequency current connected in one branch and arranged to pass through a magnetic cycle, a source of high-frequency oscillationsassociated with said coil, a translating device arranged in abranch conjugate to the low-frequency source and adapted to be responsive to changes in the hysteretic energy su plied to said coil upon receipt of the highrequency oscillations.

6. A receiver of high-frequency currents or oscillations comprising a Wheatstones bridge network, a coil in each of two branches of said network, each coil containing an iron core of large hysteresis loss, a source of lowfrequency oscillations in the battery branch of said network adapte'd to cause the iron cores to pass through a magnetic cycle, a

source of high-frequency oscillations associated with one of said coils, and a detecting'device connected in a branch of said network and adapted to respond to the lowfrequency source upon the receipt of highfrequency oscillations.

7. A receiver of high-frequency currents or oscillations comprising a balanced Wheatstones bridge network, a coil in each of two adjacent arms of saidnetwork, each coil containing a closed iron core of large hysteresis loss, a source of low-frequency oscillations in the battery branch of said network adapted to cause the iron cores to pass through a magnetic cycle, a source of highfrequency oscillations inductively associated with one of said coils, and a detecting device connected in a branch of said network conjugate to the battery branch and adapted to respond to the low-frequency source upon receipt of high-frequency oscillations.

8. A receiver of high-frequency currents or oscillations comprising a balanced Wheatstones bridge network, a coil in each of two adjacent arms of said network, each coil containing a closed iron core of large hysteresis loss, a resistance in each of the other two arms of said bridge adjusted to balance the network, a source of low-frequency oscillations in the battery branch of said network adapted to cause the iron cores to pass wit through a magnetic cycle, a source of highfreiuency osclllations inductively connected one of said coils and a detecting device connected in a branch of said network conjugate to the branch and adapted to respond to the low-frequency source upon the receipt of high-frequency oscillations.

9. A magnetic detector of high-frequency currents and oscillations comprising a Wheatstones bridge, one arm of said bridge including a coil with an iron core, said bridge bein normally balanced and being rendered un high frequency oscillations.

alanced during the receipt of 10. A magnetic detector of high-fre- 15 quency currents and oscillations comprisin a Wheatstones bridge, one arm of said bridge including a coil with an iron core, a source of low-frequency oscillations for magnetizing said iron core, said bridge being normally balanced for said low-ire uency oscillations and being rendered unba anced for said low-frequency oscillations during the receipt of high-frequency oscillations.

- In witness whereof, I hereunto subscribe 25 my name this 19th day of November A. l),

GUSTAF ELMEN. 

